A surface position detection apparatus that detects a surface position using diagonal incident light described in Japanese Laid-Open Patent Publication No. 2001-296105 and corresponding U.S. Pat. No. 6,897,462 (Patent Document 1) is known in the art as a surface position detection apparatus optimal for use as a projection exposure apparatus. To improve the detection accuracy of the surface position of a detected surface theoretically, the diagonal incident light type surface position detection apparatus is required to increase (toward 90 degrees) the incidence angle of a light beam that enters the detected surface. To prevent the structure and arrangement of a projection optical system and a condensing optical system of the surface position detection apparatus from being restricted by the detected surface, a prism having a pair of parallel inner reflection surfaces is arranged in an optical path of the projection optical system and in en optical path of the condensing optical system 50 as to arrange the projection optical system and the condensing optical system distant from the detected surface (refer to FIG. 7 in Patent Document 1).
Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-296105